This invention relates to integrated circuit fabrication, and specifically to a method of fabricating a MOS gate dielectric for separating a transistor gate from the channel between the source and drain regions.
Thermally grown SiO2 on silicon has been called the xe2x80x9cheart and soulxe2x80x9d of MOS technology. The Si/SiO2 interface has excellent semiconductor properties including low interface and bulk trapping, thermal stability, high breakdown, etc. With each successive generation of microelectronic technology, however, the thickness of the gate dielectric is scaled. e.g., becomes smaller. As the thickness is scaled below 1.5 nm, problems arise, such as excessive power consumption due to leakage from direct tunneling, boron penetration, reliability concerns, etc. Because of these problems, in the near future, possibly as early as the 80 nm node in 2005, the reign of SiO2 as a gate dielectric may dwindle, eventually coming to an end. SiO2 will likely be replaced by a higher dielectric constant (xcexa) material, which will have a greater thickness for any given capacitance.
Despite this compelling near term need for an SiO2 substitute, a suitable replacement still has not been discovered. Requirements for this replacement material include lower leakage, low interface traps, low trapped charge, good reliability, good thermal stability, conformal deposition, etc. Promising candidate materials include metal oxides such as HfO2, ZrO2, etc., and other metal oxides.
It is crucial to avoid a low-xcexa interfacial layer when depositing a high-xcexa film, as even a very thin low-xcexa layer can negate most of the benefits of the overlying high-xcexa material. It is therefore essential to deposit a high-xcexa material directly on H-terminated silicon layer.
Because of the requirements for conformality and thickness control, atomic layer deposition (ALD) has emerged as one of the most promising deposition techniques for high-xcexa material. In this technique, dielectric material is built up layer-by-layer in a self-limiting fashion, i.e., the deposition phenominnon where only one monolayer of a chemical species will adsorb onto a given surface. Currently, the leading ALD precursors for depositing metal oxides are metal halides and metal organics. There has also been some experimentation using anhydrous metal nitrates as high-xcexa dielectric precursors.
A film of ZrO2, deposited using a metal chloride precursor, such as ZrCl4 have shown good insulating properties, including a high-xcexa dielectric constant and low leakage. A major drawback of ZrCl4, however, is that it does not provide for smooth deposition directly on H-terminated silicon, requires several xe2x80x9cincubationxe2x80x9d cycles, and requires a thin layer of SiO2 for uniform initiation. These problems must be solved before metal-chloride precursors can be used in production.
A drawback of the metal organic precursors is the potential for organic contamination. Hf(NO3)4 has been demonstrated as a viable ALD precursor, as identified in the above-identified related Application, and in Conley, Jr., et al., Atomic Layer Deposition of Hafnium Oxide Using Anhydrous Hafnium Nitrate, Electrochem. and Sol. State Lett. 5 (5) May, 2002. The primary benefit of Hf(NO3)4 is that it allows deposition initiation directly on H-terminated silicon, resulting in a uniform thin layer. This method has the potential to avoid a low-xcexa interfacial layer, however, experimental work has shown that HfO2 films deposited via ALD of Hf(NO3)4 have a dielectric constant which is lower than expected, possibly because of the oxygen-rich nature of the films. The xe2x80x9cbulkxe2x80x9d dielectric properties of the resulting films must be improved before metal-nitrate precursors can find widespread use.
A method of forming a layer of high-xcexa dielectric material in an integrated circuit includes preparing a silicon substrate; depositing a first layer of metal oxide using ALD with a metal nitrate precursor; depositing another layer of metal oxide using ALD with a metal chloride precursor; and completing the integrated circuit.
It is an object of the invention to deposit a metal oxide high-xcexa layer on a silicon substrate.
Another object of the invention is to deposit a metal oxide high-xcexa layer on a silicon substrate without the requirement of forming a low-xcexa interfacial layer on the silicon substrate.
A further object of the invention is to provide a high-xcexa layer having low leakage properties.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.